Such a continuous method is known from EP 30 09 229 A1. This prior art method in particular aims at improving a comminuting method as described in EP 0 084 383 A1, whereby in the latter method a single grain and material bed comminution takes place. This improvement is in particular that the ground material agglomerates present after material bed comminution undergo disintegration. This seeks to remove the fines contained in the agglomerates by means of a classifying process, so that the overall process can be made more economic, whilst incorporating the following further comminution.
The material bed roller mills conventionally used for simultaneous single grain and material bed comminution have the advantage that they permit relatively fine-grain grinding and particles of 2 mm can be obtained. However, apart from the aforementioned disadvantage of agglomeration, an even greater disadvantage is that coarser ground material particles pass through the material bed roller mill. In addition, compared with other mills or crushers, a material bed roller mill requires relatively high capital costs.
The coarse particles passing through the material bed roller mill make it necessary for the e.g. following comminution by means of a gravity mill and in particular a tube mill to have relatively large diameter grinding elements. Large steel balls are consequently made necessary by the coarse particles passing through a material bed roller mill. In addition, in the case of the tube mill following the material bed roller mill it has been necessary to work with filling levels of approximately 26 to 30%, particularly because on reducing the filling level to e.g. 20%, there is a risk of the relatively coarse steel balls with such a low filling or grinding level shattering the jacket armour plates, as well as the slotted and front plates.
These disadvantageous aspects of the operation of a material bed roller mill and the necessary grinding element size, whilst also taking account of the degree of filling, have led to a comparatively poor efficiency with respect to the overall energy consumption, as in known installations.